Can top and method of making same



June 20, 1967 E. C. FRAZE 3,326,405

CAN TOP AND METHOD OF MAKING SAME Filed Jan. 21, 1965 2 Sheets-Sheet 1 K 4a Coin/h 4 W June 20, 1967 c FRAZE 3,326,405

CAN TOP AND METHOD OF MAKING SAME Filed Jan. 21, 1965 2 Sheets-Sheet 2 5 frar United States Patent 3,326,405 CAN TOP AND METHOD OF MAKING SAME Ermal C. Fraze, 355 W. Stroop Road, Dayton, Ohio 45429 Filed Jan. 21, 1965, Ser. No. 426,971 16 Claims. (Cl. 220-54) This invention rel-ates to a container having a portion of its wall weakened to serve as a tear strip and having a tab attached to the tear strip to serve as a handle for severing the tear strip.

The invention is directed to the solution of a specific problem that arises in the use of a met-a1 can for a highly carbonated beverage that exerts exceptionally high fluid pressure against the can wall, especially when the liquid content is agitated and/ or warmed by hot weather. When the severance of the tear strip is initiated in a conventional can of this type containing fluid under exceedingly high gaseous pressure, too often the initially escaping fluid projects the whole tear strip away from the can at high velocity in a hazardous manner.

It has been found that the primary reason for the violent separation of the tear strip from an easy opening can top of the usual construction is that the tab lies directly in the path of the high velocity fluid to receive its full impact and at the moment of impact the tab is rigidly related to the tear strip. In effect the tab is a rigid extension of the tear strip and consequently transmits the full force to the tear strip.

Apparently another factor involved in the instantaneous projection of the tear strip away from the can is that once the tearing action is initiated by peeling action at the leading end of the tear strip, there is relatively little resistance to continuation of the peeling action along the whole length of the tear strip. Another factor is that when a tab is lifted to initiate the severance of the leading end of a conventional tear strip, the tab is directly in the path of the high velocity gaseous stream that is initially released, with the consequence that the force of the stream is transmitted to the tear strip to tend to complete the tearing action. A third factor is that when the leading end of a conventional tear strip is severed by the manual movement of swinging the tab outward from the container, there is a natural tendency to follow through the swinging of the tab in such manner as to continue the peeling action for the full length of the tear strip.

The present invention solves this problem of the hazandous projection of the tear strip and does so primarily by a new relationship between the tab and the tear strip, by virtue of which the tab is only hingedly connected to the tear strip when initial severance of the leading end of the tear strip occurs. If the full impact of the released fluid is against the tab, the tab is free to yield by swinging action instead of rigidly transmitting the force to the tear strip. The problem is further solved by providing a tear strip in which the leading end of the tear strip is constructed for exceedingly easy severance but in which the portion of the tear immediately adjacent the leading end is constructed for greater resistance to severance. Thus when the leading end of the tear strip is initially severed to relieve the fluid pressure in the can, the adjacent portion of the tear strip serves, in effect, as a moderate barrier to discourage immediate extension of the tearing action.

To contribute further to the solution of the problem, the invention provides a tab construction which requires two distinct manual operations in sequence. The first operation serves merely to rupture of the can wall sufficiently for the preliminary release of the fluid pressure and the second operation carries out the severance of the tear strip, the two operations being different so that 3,326,405 Patented June 20, 1967 ice there is no tendency for the operator to carry out the two operations in one manual movement.

The first operation for initiating release of fluid pressure consists simply of lifting the tab with the tab functioning as a second class lever to rupture the can Wall with a snap action. Initial rupture of the can wall with consequent initial escape of the pressurized fluid finds the tab only hingedly connected to the tear strip. To carry out the second operation for completing the severance of the tear strip, the tab is employed as a handle to pull the rest of the tear strip free from the can.

A number of provisions make it exceedingly easy to initiate severance of the leading end of the tear strip. The construction of the tab as a second class lever is one of these provisions whereby the force applied to the swinging end of the lever is multiplied at the fulcrum end of the lever. Another provision is rounding the fulcrum end of the lever for a force-multiplying cam action against the wall of the can. Another provision is the narrowing of the leading end of the tear strip to reduce the extent of the line of scoring along which the metal must be ruptured to initiate severance of the tear strip. Still another provision is the scoring of the leading end of the tear strip in such a manner as to leave an exceedingly thin residual web of metal that is easy to tear. Preferably the metal is coined in the region of the score around the leading end of the tear strip to toughen the metal by work-hardening and thereby increase the strength of the exceedingly thin residual web.

It has been found that such a thin residual web of metal along the scoring around the leading end of the tear strip is adequate to withstand the relatively high fluid pressure before the can is opened, not only because the thin web is work-hardened but also because the narrowing of the leading end of the tear strip reduces the area of the leading end of the tear strip and theerby reduces the force exerted on the leading end by the confined pressurized fluid. In other words, narrowing the leading end of the tear strip reduces the ratio between the area of the leading end and the length of the score line around the leading end.

In one practice of'the invention it is contemplated that the tab will be connected to the tear strip at two spaced points in any suitable manner, for example, by adhesive bonding or by spot welding. In the preferred practice of the invention described herein, however, the narrowed leading end of the tear strip is formed with a hollow rivet of relatively small diameter and the adjacent wider portion of the tear strip is formed with a hollow rivet of relatively larger diameter. If desired, the two rivets may be of the same size. The tab comprises a single piece of sheet metal that is divided into a minor end portion and a major handle portion, the latter of which serves as a second class lever, the two portions being divided by a transverse line along which the metal bends when the lever is operated. The minor end of the tab is connected to the tear strip by the two hollow rivets, and the second class lever that is formed by the handle portion of the tab has a forked fulcrum end which straddles the smaller rivet outside of the area of the tear strip. When the bandle end of the tab is swung outward for the lever action on the smaller rivet, the handle acts with a high mechanical advantage to lift the small rivet and thereby sever the leading end of the tear strip.

While the lifting of the handle portion of the tab through an arc is highly effective to initiate severance of the tear strip, the severance does not extend beyond the narrow leading end for two reasons. In the first place, even if the handle is swung through the maximum arc of either manually or by impact of the escaping fluid, the lever action is confined to the leading end of the tear strip and does not extend to the adjacent large rivet. In the second place, once severance of the leading end of the tear strip is initiated by snapping the small rivet, the tab is only hingedly connected to the tear strip. In the third place, a moderate but effective barrier against extension of the severance action exists because the residual web of metal left by the scoring is thicker in the region of the larger rivet than in the region of thesmaller rivet. In addition, the larger rivet serves as a means to stiffen the tear strip locally and this fact in itself discourages further initial severance of the tear strip beyond its leading end by peeling action.

An unexpected advantage of the described construction is that attaching the tab to the tear strip at two spaced poins causes the tab to stiffen he can top and the provision of the two hollow rivets adds further reinforcement. Thus, the new construction reduces the degree to which the can top bulges in response to internal fluid pressure. Or, if it is not important to reduce the bulge, the can may be made of thinner sheet stock for a substantial cost sav- In a second practice of the invention, the smaller of the two rivets, which may be termed the first rivet, is surrounded by a closed line of scoring to permit the smaller rivet to be severed from the sheet metal wall of the container independently of severance of the tear strip by the larger or second rivet. Thus the first rivet serves as means to rupture the container wall for preliminary release of pressurized fluid in advance of severance of the tear strip by the second rivet.

A feature of the invention is the manner of processing the sheet metal to provide the exceedingly thin web of residual metal along the score line in the region of the leading end of the tear strip. In this regard, the invention ischaracterized by the concept of coining the sheet metal to reduce its thickness prior to scoring the metal. It is this two-step procedure that makes it possible to reduce the sheet metal to the exceedingly thin residual web. For example, an aluminum wall having a thickness of .015" may be coined to reduce the thickness of the wall to as little as .006 and then the coined metal may be scored to a depth of .003" to leave a residual web of metal of a thickness of only .003.

The features and advantages of the invention may be understood from the following description together with the accompanying drawings.

In the drawings, which are to be regarded as merely illustrative:

FIG. 1 is a fragmentary plan view of an aluminum can top embodying the presently preferred practice of the invention;

FIG. 2 is a simplified sectional view showing how dies may be employed to form a dimple in the can top in preparation for forming the two hollow rivets;

FIG. 3 is a similar simplified sectional view showing how a pair of dies may be used to convert the dimple into a relatively small hollow rivet and an adjacent relatively large hollow rivet, the dies further functioning to thin' the metal by coining around both of the rivets;

FIG. 4 is an enlarged fragmentary plan view of the can top in the region of the two hollow rivets after the operation of FIG. 3, showing how the metal is reduced in thickness by coining around each of the rivets;

FIG. 5 is a plan view similar to FIG. 4 showing how the metal is scored by the next operation to form the tear strip with the scoring extending into the coined area;

FIG. 6 is a sectional view illustrating the next step of positioning a tab on the can top with the two hollow rivets of the tear strip extending through flanged apertures in the tab;

'- FIG. 7 is a similar view showing the two rivets headed into permanent engagement with the tab; 7

FIG. 8 is a fragmentary sectional view of the finished can top showing the tab in its normal starting position adjacent the can top;

FIG. 9 is a similar view showing how swinging the tab outward results in lifting the small rivet to sever the leading end of the tear strip with a snap action; and

FIG. 10 is a view similar to FIG. 5 showing a different pattern for the scoring of the can top.

FIG. 1 illustrating the presently preferred embodiment of the invention shows a can top 10 which, in this instance, is made of an aluminum alloy of a thickness of approximately .015 and is intended to serve as the top of a can that confines a highly charged beverage, for example, beer or a highly carbonated soft drink. The can top 10 is scored along a continuous score line 12 to form a tear strip 14, which, as shown, perferably has a leading end that is narrowed for reduction in the area that is subjected to the internal fluid pressure.

A tab to facilitate manual removal of the tear strip 14 is made from a single piece of sheet metal and is divided along a transverse bend line 15 into a minor end portion 16 and a major longitudinal handle portion, which latter portion constitutes a second class lever 20. The lever 20 is, in effect, hingedly connected to the end portion 16 along the bend line 15 and is of a forked configuration that provides two fulcrum ends 22 that straddle the leading end of the tear strip 14.

The end portion 16 of the tab is suitably connected to the tear strip 14 at two points, one point being in the small area of the leading end of the tear strip and the second point being spaced from the first point but close to the leading end. By virtue of this arrangement the lever 20' may be swung about the bend line 15 as an axis to sever the leading end of the tear strip from the can top with a snap action and then the lever may be used as a handle for a second and distinctly different operation in which the rest of the tear strip is pulled free from the can top.

In the construction shown, the lever 20 is stiffened throughout its length by a U-shaped marginal rib 24 that is formed by offsetting the sheet metal. Preferably, the free end of the lever is offset and folded back On itself as shown at 25 in FIG. 8. In the construction shown, the central area of the lever is offset at several spaced points to form small sharp bosses or hobnails 26 to facilitate frictional gripping of the lever. To form the two fulcrum ends, two small apertures 28 are provided on the bend line 15 and corresponding slits or slots 30 extend from the respective apertures to the fulcrum ends 22 to free the fulcrum ends from the end portion 16 of the tab. As showns in FIGS. 8 and 9, each of the fulcrum ends 22 may be formed with a rounded nose 32 to provide cam action against the can top when the lever is lifted.

Although the tab may be connected to the two points of the tear strip 14 in any suitable manner within the scope of the invention, it is advantageous to attach the tab by means of two spaced hollow rivets that are formed in the material of the tear strip and extend through corresponding apertures in the tab. Thus, FIGS. 1 and 7 show a rivet 34 of relatively small diameter formed in the narrow leading end of the tear strip 14 and extending, through a corresponding aperture in the tab and show a second rivet 35 of largerdiameter formed in the tear strip close to the small rivet and extending through a corresponding larger aperture in the tab. Preferably, but not necessarily, the two apertures in the tab are flanged to provide collars or hubs that snugly embrace the two rivets, a hub 36 embracing and reinforcing the smaller rivet 34 and a hub 38 embracing and reinforcing the larger rivet 35. An advantage of this construction is that the two hubs 36 and 38 form a sturdy hollow rib 39 between the two rivets.

The preferred method of forming the two rivets 34 and 35 is illustrated by FIGS. 2, 3, 6 and 7. FIG. 2 illustrates the first step of forming a dimple 40 in the can top in the region of the leading end of the tear strip before the can top is scored, the dimple being of a sufficiently large diameter to include the areas of both of the two rivets that are to be formed in the tear strip. In the formation of the dimple 40, the sheet metal of the can top is bulged by a lower male die 42 into a circular cavity 44 of an upper die 45 while a surrounding pressure pad 46 under the action of springs 48 holds the sheet metal against the upper die with sufiiciently light pressure to permit the sheet metal to slip freely radially inwardly towards the cavity 44. This operation results in forming the dimple without appreciable thinning of the sheet metal and actually results in increasing the amount of sheet metal within the area in plan of the dimple.

FIG. 3 illustrates the second step of forming the two rivets and of simultaneously coining the sheet metal in annular areas around the two rivets. In FIG. 3 an upper die 50 has a relatively small cavity 52 to form the rivet 34 and has a relatively large cavity 54 to form the larger rivet 35, each cavity having a communicating vent passage 55. The rim of the small cavity 52 is formed with a circular land 56 for the purpose of reducing the thickness of the can top by a coining operation and the larger cavity is formed with a similar land 58 that is interrupted by the land 56. The combined areas of coining around the two rivets is defined by a continuous tapered shoulder 59 in FIG. 4 and the deeper coining around the smaller rivet forms a shoulder 60 at the boundary of the less severe coining around the larger rivet.

With the aluminum alloy of the can top of an initial thickness of .015", it is contemplated that the coining land 56 around the small cavity will be dimensioned to reduce the thickness of the sheet metal to .006" and the land 58 around the larger aperture will be dimensioned for less drastic reduction to a thickness of approximately .009". Consequently, the coining operation results in forming a step from the thinner coined area to the thicker coined area, the step being indicated by the arcuate line 60 in FIG. 4.

The upper die 50 is surrounded by an upper pressure pad 62 which cooperates with a lower pressure pad 64 to hold the sheet metal firmly without slippage during the forming operation. A lower die 65 which cooperates with the upper die 50 has a small diameter boss 66 to cooperate with the small die cavity 52 to form the small rivet and has a larger boss 68 to cooperate with the larger die cavity 54 to form the larger rivet.

When the two dies 50 and 65 close on the dimple 40 of the can top, the metal is forced into the two cavities of the upper die and it is important to note that the two cavities are dimensioned for headroom or clearance to avoid confining the metal that forms the transverse end Walls of the rivets. The preliminary formation of the dimple increases the amount of metal available for forming the two rivets with the consequence that the walls of the two rivets are thicker by reason of the dimple. It is to be further noted that the coining operation which occurs simultaneously with the formation of the rivets displaces metal radially inwardly towards each rivet to add metal to the rivet. Since the metal is confined in all regions except in the upper clearance spaces of the two die cavities 52 and 54, the metal displaced by the coining operation tends to follow the line of least resistance to flow into the clearance spaces of the cavities to increase the height or axial dimension of the two rivets. This effect is accentuated in the region of the smaller cavity 52 by reason of its small cross-sectional area. Thus, actually the two rivets are each formed in part by the coining operation.

The next operation is to score the metal along the previously mentioned score line 12 by a suitable scoring tool (not shown) which is constructed to penetrate the metal to .a depth of .003" in the two coined regions of the can top and to penetrate to greater depth, say to a depth of .007", where the can top is not coined. It is apparent that such a coining operation reduces the sheet metal to a residual thickness of approximately .003 in the coined region around the smaller rivet 34 and reduces the thickness of the metal to a residual web of .006" in the coined region around the larger rivet, the remainder of the score line reducing the metal to a residual web of approximately .006 to .008". Thus, the metal along the score line is exceedingly thin at the leading end of the tear strip around the smaller rivet 34 and is slightly thicker adjacent the larger rivet 35.

The pattern of the scoring in the region of the leading end of the tear strip is shown in FIG. 5 where the score line 12 defines the tear strip 14. It is to be noted than an additional score line 70 completes a full circle around the smaller rivet 34 to define a small auxiliary tear strip that may be severed independently of the main tear strip.

FIG. 6 illustrates the next step of placing the minor end portion '16 of the tab in position with the two hubs 36 and 38 embracing the two rivets 34 and 35 respectively in preparation for heading the two rivets into permanent engagement with the tab. The heading operation is carried out by suitable dies (not shown) which squeeze the two transverse end walls of the two rivets to cause the rivets to expand radially and thereby form circumferential beads in engagement with the tab as shown in FIG. 7.

The manner in which the invention serves its purpose may be readily understood from the foregoing descrip tion. When the handle or free end of the lever 20 is swung upward from its initial normal position shown in FIG. 8, the two fulcrum ends 22 of the lever press against the can top outside of the area of the tear strip on opposite sides of the smaller rivet 34 with cam action in the manner shown in FIG. 9. The tab provides a force-multiplying lever action since the fulcrum ends are relatively short and a further force-multiplying effect is created by the cam action of the rounded noses 32 of the lever ends against the can top. Consequently, the upward swing of the lever creates .a high-magnitude lifting force on the near side of the small rivet to tilt the small rivet upward and thereby sever the tear strip around the small rivet to permit the confined gases to escape as indicated by the arrow 72. The severance of the metal around the small rivet is further facilitated by the fact that the small rivet fulcrums or rocks about the hollow rib 39, As may be seen in FIG. 9, the bearing of the small rivet against the hollow rib 39 as the lever is swung upward not only causes the rivet to pull free around its near side, i.e., along the end edge of the tear strip, but also pulls the metal apart in the region of the transverse score line 70 on the far side of the rivet. As a consequence, the small rivet pops free around its entire circumference with a snap action to leave the tab only hingedly connected to the tear strip. The operator then employs the tab as a handle for the second operation in which pulling force is exerted on the tab to sever the rest of the tear strip from the can top. As indicated in FIG. 9, the lever 20 swings upward through a relatively large angle, for example 60, before the small rivet pops loose for initial release of the confined pressurized fluid.

There is a natural pause between the initial lever action that initiates the severance of the tear strip and the subsequent pulling action that completes the removal of the tear strip and this natural pause between the two operations provides ample time for the fluid pressure in the can to drop to a desired degree before the final severance of the tear strip occurs.

FIG. 10 illustrates a modification of the can top construction which consists of a slightly different pattern of scoring. In FIG. 10' the can top has the usual score line 12a, but the transverse score line 70 of FIG. 5 is omitted.

In the first embodiment of the invention, the small rivet is completely severed from the sheet metal of the can top and thereafter the tab is hingedly connected to the tear strip solely by the larger rivet. Thus, in effect, the popping of the small rivet by the lever action in the first embodiment of the invention actually results in complete removal of a small area of sheet metal from the can top at the leading end of the tear strip. In the modified em- )odiment of the invention shown in FIG. 10, the snaping of the smaller rivet leaves the tab only hingedly coniected to the tear strip as usual, but the smaller rivet renains connected to the tear strip since the initial severance f the metal extends around only three sides of the small ivet. In all other respects, however, the modified em- )odiment of the invention is identical with the first deicribed embodiment.

My description in specific detail of the preferred emaodiment and the modified embodiment of the invention will suggest various changes, substitutions and other degartures from my disclosure within the spirit and scope of the appended claims.

I claim:

1, In a container for pressurized fluids having a sheet metal wall scored to form a tear strip and having a tab attached to the tear strip to serve as means for manual severance of the tear strip, the improvement comprising:

the tab having a first connection with the sheet metal wall and having a second connection with the sheet metal wall to act on the twoconnections in sequence;

at least the second connection being within the area of the tear strip for removal of the tear strip by the tab;

the sheet metal wall being weakened in the region of the first connection for severance of the sheet metal wall in said region,

whereby the tab initially severs the sheet metal in the region of the first connection for preliminary release of fluid from the container and subsequently severs the tear strip.

2. An improvement as set forth in claim 1 in which the sheet metal is scored to leave a residual web of minimum thickness in the region of the first connection to facilitate the initial severance of the leading end of the tear strip; and

in which the metal is scored to leave a thicker residual web in the region of the second connection to discourage advance of the initial severance beyond the leading end of the tear strip.

3. An improvement as set forth in claim 2 in which the tear strip is stiflened in the region of the second connection further to discourage advance of the initial severance of the tear strip.

4. An improvement as set forth in claim 1 in which the sheet metal wall is scored completely around the first connection.

5. In an easy opening container having a wall of sheet metal to confine a pressurized fluid, the combination of:

scoring in the sheet metal of a wall of the container forming a tear strip with a leading end;

a hollow rivet formed in the leading end of the tear strip;

a second hollow rivet formed in the material of the tear strip at relatively small spacing longitudinally of the tear strip from the first rivet; and

a tab connected to both of the rivets to act on the two rivets in sequence to initiate severance of the tear strip by the first rivet for initial release of fluid from the container and subsequent severance of the remainder of the tear strip by the second rivet after substantial drop in the fluid pressure in the container.

6. A combination as set forth in claim 5 in which the tab includes a second class lever hingedly connected with the first rivet, the lever being of forked construction with two fulcrum ends straddling the first rivet.

7. A combination as set forth in claim 5 in which the scoring that forms the tear strip leaves a relatively thin residual web in the region of the first rivet and leaves a substantially thicker residual web in the region of the second rivet to discourage initial severance of the tear strip beyond the first rivet.

8. In an easy opening container for pressurized fluids having a wall of sheet metal, the combination of:

a first hollow rivet formed in the sheet metal of the wall of the container;

a coined area extending around the first rivet in which area the sheet metal is reduced in thickness;

a second hollow rivet formed in the sheet metal of the wall adjacent the first rivet;

scoring in the sheet material of the wall enclosing the two rivets forming a tear strip with the first rivet at the leading end of the tear strip, said scoring extending into said coined area to leave a residual web of metal of minimum thickness; and

a tab divided by a transverse bend line into a minor end portion and a major handle portion, the end portion of the tab having two apertures corresponding to the two rivets with the two rivets extending through the two apertures in positive engagement with the tab,

said handle portion of the tab being in the form of a second class lever to hinge about the bend line, the second class lever having a forked fulcrum end straddling the leading end of the tear strip for lifting action on the first rivet.

9. A combination as set forth in claim 8 in which the first rivet is smaller in diameter than the second rivet and in which the leading end of the tear strip is narrowed in width.

10. A combination as set forth in claim 9 in which the end portion of the tab is flanged to form two hubs snugly embracing the two rivets respectively.

11. In an easy opening container for pressurized fluids having a wall of sheet metal, the combination of a first hollow rivet formed in the sheet metal of the wall of the container;

a coined area extending around the first rivet in which area the sheet metal is reduced in thickness;

a second hollow rivet formed in the sheet metal of the wall adjacent the first rivet;

a second coined area extending around the second rivet in which the sheet metal is reduced in thickness but is thicker than in the first coined area;

scoring in the sheet material of the wall enclosing the two rivets and forming a tear strip with the first rivet at the leading end of the tear strip, said scoring extending into both of the two coined areas and leaving a residual web of metal of minimum thickness in the first coined area and a residual web of metal of slightly greater thickness in the second coined area; and

a tab divided by a transverse bend line into a minor end portion and a major handle portion, the end portion of the tab having two apertures corresponding to the two rivets with the two rivets extending through the two apertures in positive engagement with the tab,

said handle portion of the tab being in the form of a second class lever to hinge about the transverse fold line, the second class lever having a forked fulcrum end straddling the leading end of the tear strip for lifting action on the first rivet.

12. In an easy opening container having a sheet metal Wall confiining a pressurized fluid, the combination of: a tab attached to the sheet metal wall by a first rivet formed in the sheet metal of the wall and by a second rivet formed in the sheet metal of the wall to apply force to the two rivets in sequence, the sheet metal wall being weakened by a continuous line of scoring surrounding the first rivet; the sheet metal wall being weakened by a line of scoring forming a tear strip with the second rivet in the area of the tear strip, whereby manipulation of the tab first ruptures the sheet metal wall in the region of the first rivet for preliminary release of pressurized fluid and then severs the tear strip.

13. In an easy opening container having a sheet metal wall to confine a pressurized fluid, the combination of:

a first hollow rivet and a second hollow rivet formed in the sheet metal wall;

scoring in the sheet metal wall forming a tear strip with at least the second hollow rivet within the area 5 of the tear strip, the sheet metal wall being weakened in the region of the first rivet; and

a tab connected to the first and second hollow rivets to act on the two hollow rivets in sequence to initially rupture the sheet metal wall in the region of 10 the first rivet for preliminary release of fluid from the container and to subsequently sever the tear strip.

14. A combination as set forth in claim 13 in which a 15. A combination as set forth in claim 13 in which the sheet metal wall is scored completely around the first rivet to permit separation of the first rivet from the container wall.

16. In the construction of an easy opening container for pressurized fluid wherein a wall of sheet material of the container is weakened to form a tear strip and a tab with a handle end is attached at its opposite end to the leading end of the tear strip for severance thereof by lifting of the tab, the improvement comprising:

a relatively small weakened portion of the sheet material outside of the area of the tear strip being attached to the tab at a point between the tear strip and the handle end 0g the tab whereby lifting of the tab initially ruptures the sheet material at said weakened portion for preliminary release of pressurized fluid in advance of severance of the tear strip.

References Cited UNITED STATES PATENTS 3,215,306 11/1965 Simpson et a1 220-54 3,221,924 12/1965 Harvey et al. 22054 3,225,957 12/1965 Huth 220-54 THERON E. CONDON, Primary Examiner. G. T. HALL, Assistant Examiner. 

1. IN A CONTAINER FOR PRESSURIZED FLUIDS HAVING A SHEET METAL WALL SCORED TO FORM A TEAR STRIP AND HAVING A TAB ATTACHED TO THE TEAR STRIP TO SERVE AS MEANS FOR MANUAL SEVERANCE OF THE TEAR STRIP, THE IMPROVEMENT COMPRISING: THE TAB HAVING A FIRST CONNECTION WITH THE SHEET METAL WALL AND HAVING SECOND CONNECTION WITH THE SHEET METAL WALL TO ACT ON THE TWO CONNECTIONS IN SEQUENCE; AT LEAST THE SECOND CONNECTION BEING WITHIN THE AREA OF THE TEAR STRIP FOR REMOVAL OF THE STRIP BY THE TAB; THE SHEET METAL WALL BEING WEAKENED IN THE REGION OF THE FIRST CONNECTION FOR SERVERANCE OF THE SHEET METAL WALL IN SAID REGION, 